This invention relates to detecting leaks in pipes which carry fluids such as water.
It is known to locate leaks in underground water pipes using so-called leak detectors, which can pinpoint leaks prior to excavating the ground.
Before using a leak detector it is normal to identify the general geographic area which is experiencing water loss. Typically, the presence of a leak is initially identified by taking readings from meters located at various water distribution points, in order to see whether there is increased consumption, especially at night.
Suspected leaks can then be located using a leak detector. However, a disadvantage of this arrangement is that it is time consuming to subsequently survey the whole of the geographical area, in which there is a suspected fluid loss, using leak localisers.
We have now devised an apparatus for detecting leaks in pipes which alleviates the above-mentioned problem.
In accordance with this invention, there is provided an apparatus for detecting leaks in pipes comprising a transducer for acoustically monitoring the pipe, means for analysing a parameter of the output signal of the transducer and for generating an alarm signal, in the event that the parameter is above a maximum value or below a minimum value and means for outputting said alarm signal.
In use, a plurality of apparatus in accordance with this invention can be temporarily or permanently installed to pipes at various locations around a geographical area of supply. Thus, once a leak has been identified in an area, it is a relatively simple matter to more precisely determine where in the area should be surveyed, by monitoring at the remote receiver for an alarm signal. Accordingly, it will be appreciated that the need to survey the whole of the area is avoided.
In one embodiment, the alarm signal output means comprises a transmitter, such as a radio transmitter, which transmits a wireless alarm signal to a remote receiver.
The remote receiver may comprise means for logging the position where the alarm signal is received. Thus, for example, receivers may be mounted on delivery vehicles, which frequently drive around areas. Data is then downloaded from the receivers on a regular basis, with the precise location of any detected alarm signals being recorded. Preferably, the position logging means receives signals from a global position satellite.
In a second embodiment, the alarm signal output means may be arranged to transmit the alarm signal along a cable to the remote receiver. In a third embodiment, the alarm signal output means comprises an optical or audible transducer.
Preferably, the transmitting means transmits a low power radio signal, thereby conserving the battery power of the apparatus and enabling a plurality of apparatus to transmit on the same frequency, without the risk of interference.
In use, an alarm signal can be detected by moving or by driving around the geographical area with a remote receiver unit, until an alarm signal is detected; the point of the leak can then be pinpointed using a conventional leak detector.
Preferably, the transmitter is arranged to transmit a different standby signal when said parameter is not above said maximum value or below said minimum value. Thus, it will be apparent that the apparatus may not be working correctly, when neither the standby signal nor the alarm signal is detected at the remote receiver.
Preferably, the transmitter only transmits a signal periodically, in order to further conserve battery power.
Preferably, the alarm signal is transmitted more frequently than the standby signal, so that the alarm signal is less likely to be overlooked whilst moving or driving around the area.
The most common way of localising leaks is achieved using the correlation principle, in which two acoustic transducers are mounted at different points on the pipe under analysis. A correlator then compares the noise detected at the two sensor points and determines the difference between the time which the noise takes to reach one sensor compared with the time which it takes to reach the other sensor. Thus, the leak position can be determined from the following formula:   L  =            D      -              (                  V          xc3x97                      T            d                          )              2  
where:
L=leak position
D=distance between the sensors
V=velocity of sound for pipe under consideration
Td=time delay between noise signals.
It is difficult and time consuming to attach the acoustic transducers of a leak localiser to the pipe each time a measurement is taken and it will be appreciated that it is sometimes necessary to reposition the transducers and take several new measurements before the leak can be pinpointed.
Thus, preferably, the apparatus comprises a port for providing an external connection to its acoustic transducer. In use, once an alarm signal has been detected by one of the apparatus, the leak can be pinpointed by connecting a correlator to the respective ports of two leak detection apparatus in accordance with this invention. The correlator then uses the acoustic transducers of the two apparatus to take its measurements and accordingly measurements can be taken far more easily and quickly, since no time needs to be spent connecting separate acoustic transducers to the pipe.
Preferably, the port comprises a transmitter which provides a wireless link to a corresponding port of the leak localiser. In this manner, the apparatus can be provided with a completely sealed body, so that the ingress of fluid can be prevented.
Leaks in pipes generate a noise and this noise can be detected when there is a leak. However, a problem of detecting leaks in this manner is that the noise created by normal fluid consumption can mask the noise created by the leak. Thus, preferably, the apparatus comprises a clock, the analysing means being arranged to analyse the parameter of the output signal of the transducer at night, when little or no fluid consumption normally occurs.
All pipes have different noise characteristics from each other. Hence, the noise level indicating a leak will vary greatly throughout the geographical area. This problem is further exacerbated by the fact that plastics pipes do not conduct sound as well as metal pipes.
Accordingly, it will be appreciated that it is not possible to reliably detect for a leak at different locations by merely comparing the value of the parameter of the output of the transducer at each location with the same maximum and/or minimum value.
In order to overcome this problem, the analysing means is preferably arranged to periodically measure the output level of the transducer and to provide an average of previously measured levels, the monitoring means being further arranged to determine said maximum and/or minimum values from said average. In this manner, the level at which the alarm signal is triggered at each location is dependent upon the average of previous noise values at that location.
Preferably, an alarm signal is also generated, in the event that the parameter is above an absolute maximum value or below an absolute minimum value.
A disadvantage of using average values to determine the maximum or minimum values is that the readings used in the average calculation could include readings which are representative of a leak and this could mean that some leaks go undetected. In order to prevent this, the monitoring means is preferably arranged to reject readings from the average calculation which are above a maximum threshold value or below a minimum threshold value.
The maximum and/or minimum threshold values should themselves vary between locations, in order to take account of the different surroundings. Accordingly, the monitoring means is preferably arranged to reject readings from the average calculation which are a predetermined amount more or less than the median of the stored readings.
In order to prevent intermittent noise from triggering an alarm, the monitoring means is preferably arranged to only produce an alarm signal if a reading which is above said maximum limit or below said minimum limit is not substantially different from an adjacent reading.
Preferably, the monitoring means is arranged to take a series of measurements of the output level of the transducer, the monitoring means being arranged to compare the level that has been exceeded for a predetermined percentage number of readings with said maximum or minimum values and/or to compare the spread between levels which have exceeded predetermined upper and lower percentage numbers of readings.
Known acoustic transducers can be mounted inside a body which is screwed to a fitting in the pipe. However, a disadvantage of this arrangement is that air needs to bled out of the body, so that the acoustic transducer is fully in contact with the fluid in the pipe.
Air is carried along with fluid flowing along pipes and this air can collect in closed cavities in the pipe. Accordingly, a leak detection apparatus in accordance with this invention may cease to operate correctly, unless the cavity in which its transducer is mounted is regularly bled of air.
In one embodiment, an air bleed valve is mounted in a flow passage through a body of the apparatus, sensing means being provided for opening said valve, when a build up of air is sensed in the flow passage.
Alternatively, in accordance with this invention, as seen from a second aspect, there is provided an assembly comprising a transducer for acoustically monitoring fluid flowing along a pipe, the assembly comprising a body having a port for connecting to a corresponding port in the wall of the pipe, a fluid-flow passage extending through the body and having opposite ends communicating with the port, an acoustic transducer mounted inside the flow passage, and flow diverting means for diverting at least some of the fluid flowing along the pipe through said flow passage.
In use, the assembly is attached as a spur to a conventional port in the pipe, with at least some of the fluid in the pipe being branched off through the passageway. Thus, the body is continually flushed by the fluid and hence air cannot build up around the transducer. Furthermore, the fluid flushes out any air which is present in the body when the apparatus is first installed.
Preferably, the flow diverting means is arranged to divert all of the fluid flowing along the pipe under analysis through the passageway.
These and other objects, features, and advantages of the present invention will be clearly understood through consideration of the following detailed description.